Process and device for the separation of viscoplastic materials such as plastics from materials such as paper which can be defibrated by mechanical action

ABSTRACT

The invention relates to a process for separating tenaciously elastic materials such as plastics and rubber from materials tearing and/or defiberizing under high mechanical stress, particularly paper, and to a device for performing said process. The process is characterized in that the mixture of materials to be separated is subjected to high radial, axial and tangential acceleration forces, whereby a mass flow of shredded fibrous material and a mass flow of substantially unshredded plastics is withdrawn separately. The device for performing the process consists of a screen basket which is cylindrical or preferably polygonal in shape and has borings in its jacket to let the defiberized material pass through, a rotatable driving shaft being arranged coaxially inside the screen basket, with blades being attached to said driving shaft, preferably in rigid connection.

FIELD OF THE INVENTION

The invention relates to a process and a device for the separation ofmaterials which are tenaciously elastic at normal temperatuze, such asplastics and rubber, from other materials defiberizing under highmechanical stress, such as paper, cardboard, carton or other productscontaining cellulose fibers.

More specifically, in waste disposal and recovery of substancescontained in the waste materials, the separation of plastics and paperrepresents a considerable problem. Such mixed waste containing bothplastics and paper or other cellulose products arises in huge amounts.Thus, for example, the presorted plastic packages from the collectionsconducted by Duales System (Germany), and particularly the so-calledmixed fraction, have a significant percentage of paper, including paperlabels, erroneous classifications in sorting, and paper-plasticcomposite materials.

To date, the separation of plastics, rubber and other tenaciouslyelastic materials from materials containing cellulose fibers, such aspaper, cardboard and carton has been effected using the wet separationprocess which works by extensive defiberization of the fiber matrix andsubsequent separation resulting in at least two streams of material,namely, the cellulose-containing sludge having a high water content, andthe water-insoluble plastics. This process requires a considerable inputin energy and machinery. In the above case, the paper defiberization isperformed in a wet-grinding mill, for example, and in the shreddingprocedure, water is added exceeding the weight of plastics and paper bya multiple. Here, in particular, a huge amount of energy is required toset the masses of water in motion. So-called friction separators areused to separate the arising sludge of fillers, contaminants or othersubstances from the plastics. In each case, the mass flow rich in fibersmust be dehydrated using vibrating or bottom screens, for example. Inaddition, the water content is usually reduced by pressing such aschamber filter pressing; however, a water content as high as more than50% still remains in the product. If the mass high in paper fiberscannot be utilized, which is the normal case with waste materials, thehigh water content either causes high costs for dumping or considerableexpenditure for drying in case of thermal utilization of the wastematerials. Similarly, the plastics must be dehydrated, particularly ifthey are high in foils as is the case, e.g., with the combination of theabundant polyethylene foils with paper, which is predominantly effectedby means of mechanical dryers. To this end, modified centrifuges orwhizzers are used. In some cases, thermal (after) drying may be requiredso that in total, the expenditure for separation causes considerablecost and is ecologically unfavorable due to the high input in energy.

Numerous investigations have been conducted in this field. As examples,there may be mentioned: Louis Jetten, Stoffliches Kunststoffrecyclingund die Rolle des Wassers in Aufbereitungstechnik beim Verwerten vonKunststoffen, VDI-Verlag, Düsseldorf, 1993; and technological study:Stoffliches Kunststoffrecycling, Part 2, edited by EWvK,Entwicklungsgesellschaft für die Wiederverwertung von Kunststoffen,Wiesbaden, 1992.

Furthermore, processes for dry separation of paper and plastics operatedutilizing electrostatic charging are already known. Here, separationusing a gravity separator may be mentioned, which is described in DE3,227,874 and DE 4,225,977, for example. This process involvesconsiderable drawbacks. The charging material is required to meet quitespecific preconditions regarding the geometrical dimensions. Also, thedemands with respect to the drying level are very high. The operativeinput is considerable. Moreover, this process does not permit separationof non-positive and positive composite materials.

SUMMARY OF THE INVENTION

Therefore, it is the object of the invention to provide a process forthe separation of tenaciously elastic materials such as plastics andrubber from materials defiberizing under high mechanical stress, such aspaper, cardboard and carton, which is advantageous in ecological termsand simple in processing technology. For example, LDPE, HDPE, PP,polystyrene, PVC, PET, and ABS may be mentioned as plastics.

Surprisingly, it was found possible to separate tenaciously elasticmaterials such as plastics and rubber from fiber-containing materialssuch as paper in an essentially dry and technically simple fashion byimpinging the mixture of plastics and fiber-containing material usinghigh acceleration and impact forces, the fiber-containing material beingripped and/or defiberized by the action of said forces, dischargingthrough the appropriate openings of a screen basket, while thenon-defiberizing plastics remain in the interior of the casing and areremoved in axial direction. The application of acceleration and impactforces or the use of a centrifuge in the dry separation of paper andplastics must be rated surprising because centrifuges have invariablybeen used for separating solid-liquid phases or liquid-liquid phases.

BRIEF DESCRIPTION OF THE FIGURES

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 shows a longitudinal section through a device for performing thepresent invention; and

FIG. 2 represents a cross-section through FIG. 1 along the line AA′.

DETAILED DESCRIPTION OF THE PREFERRED EMRODIMENTS

Thus, the invention is directed to a process for separating tenaciouslyelastic materials such as plastics and rubber from materials tearingand/or defiberizing under high mechanical stress, particularly paper butalso other fibrous materials, which process is characterized in that themixture of materials to be separated, preferably following previousshredding, is subjected to high acceleration forces in radial, axial andtangential directions.

Preferably, the material to be separated is pre-shredded to a size of≦50 mm.

Furthermore, the invention is directed to a device for performing theprocess, consisting of a closed screen basket (1) which is cylindricalor preferably polygonal in shape and has multiple borings or openings(2), a rotatable driving shaft (3) being arranged coaxially inside thescreen basket (1), with blades (4) being attached to said driving shaft,preferably in rigid connection. The driving shaft is driven, e.g.,through a flange (5) with belt drive, using an electric motor (notdepicted). The blade diameter is of such relative dimension so as toleave a gap between the blade end and the casing. Depending on geometry,the size of the materials to be shredded may be varied.

At the charging side, the first blades in the casing are smaller indiameter than the following blades, so that the charged material mixtureto be separated has a better distribution within the casing.

The casing and the interior rotating shaft with blades are arranged in abox (6) having a charging inlet (7) for the material mixture to beseparated, and an outlet (8) at the other end for the plastics remainingin the drum and being conveyed by the rotating blades. In addition, thebox (6) has an outlet (9) for the removed paper. For improved removal ofthe paper, a circumferentially revolving scraper (not depicted) may beprovided.

Preferably, the casing as well as driving shaft and blades are made ofhigh-strength and corrosion-resistant material such as stainless steel.

Preferably, the borings (2) or outlets at the periphery of the screenbasket (1) have sharp edges (not depicted!) serving for improveddefiberization of the shredded paper hurled in outward direction throughthe boring of the casing against the screen basket (1), the screenbasket (1) being supported by the exterior walls of box (6).

The blades are preferably inclined to ensure motion of the particles inaxial direction with sufficient residence time in the device. For theplastics mixed fraction from Duales System, for example, inclinationangles ranging from 5 to 7 degrees are suitable.

The interior bladed shaft rotates at a speed ranging from 1,000 to2,000, preferably from 1,200 to 1,800 revolutions/minute, the number ofrevolutions being adjusted as a function of the material mixtureemployed. The residence time is from 10 s to 2 min.

The separation effect is improved when the paper is moistened prior tobeing charged into the separation device, with moisture contents of from3 to 20% relative to the total mass of paper and plastics having provenuseful. Nevertheless, the process according to the invention remains adry process because in the well-known wet processes, the water contentis always more than 50%, preferably more than 70%.

Depending on grain size of the charging material and desired separationlevel, the outlet size varies between 2 and 7 mm.

The preferred shape of the screen basket (1) is a polygon which may haveisosceles or non-isosceles planes. It was found that if the screenbasket is composed of polygon-like planes, the separation effect issubstantially improved as compared to a cylindrical screen basket.

Referring to the appended drawings, the function of process and devicewill be exemplified, wherein

FIG. 1 is a longitudinal section through a device for performing theprocess, and

FIG. 2 represents a cross-section through FIG. 1 along the line AA′.

The solids mixture of plastics and paper is charged through the charginginlet (7) and distributed inside the screen basket by the first bladeswhich have a smaller diameter than the following blades (4). The shaft(3) with blades (4) which is set in rotation by a drive not depictedcauses the particles to undergo acceleration and impact which eventuallyresults in accumulation of the defiberized paper at the screen basket(1) and subsequently, discharge through the borings (2). Simultaneously,the plastics migrate in axial direction and are removed through outlet(8). Paper accumulating in the volume defined by box (6) and screenbasket (1) is withdrawn via outlet (9), using pneumatic exhaustion (notdepicted).

For example, a device according to the invention has the followingdimensions: length: 1,500 mm, blade diameter: 950 mm (variable), widthof gap between blade ends and casing wall, depending on shape of thecasing: 25 mm at maximum, number of blades: 4×11, power input of thedevice: 50-80 kW; screen basket outlets: 5, throughput: 1 ton per hour.

EXAMPLE

A solids mixture consisting of 90.4% of package foils and 9.6% of coatedpaper is shredded using a mill with a screen basket having a diameter of50 mm. There is uniform distribution of the paper within the plastic,and the mixture is dry. After a first run wherein the mixture is passedthrough the device, the following separation results are obtained:

Results of the First Run:

High-grade Low-grade fraction (%) fraction (%) Yield 93.5 6.5 Papercontent 6.9 47.9 Plastics content 93.1 52.1

When recharging the high-grade fraction from the above result, thefollowing separation results are obtained:

Results of the Second Run:

High-grade Low-grade fraction (%) fraction (%) Yield 96.4 3.6 Papercontent 4.5 71.5 Plastics content 95.5 28.5

Thus, in two runs, a total of 57.6% of the charged paper is removed, theyield being 90.1%.

What is claimed is:
 1. A process for the dry separation of viscoplasticmaterials from materials defiberizing under mechanical stress, whereinthe materials to be separated are subjected to high acceleration andimpact forces in radial, axial and tangential directions, and a massflow of fibrous material and a mass flow of viscoplastic materials arewithdrawn separately, and wherein said viscoplastic materials and saidmaterials defiberizing under mechanical stress are present essentiallyas composite materials, and only the fibrous material will bedefiberized under the action of said forces and separated from theviscoplastic material, the viscoplastic materials being withdrawn in aseparate mass flow in an essentially non-shredded state, wherein saidhigh acceleration and impact forces are imparted with a deviceconsisting of a screen basket having borings or outlets in a jacket,allowing the defiberized material to pass through, a rotatable drivingshaft being arranged coaxially in an inner zone of the screen basket,with blades being attached to said driving shaft, so that depending onthe number of blades, an inclination of the blades and a length of thescreen basket only the fibrous material will be defiberized andseparated from the viscoplastic material, wherein the screen basket hasa cross section in a plane perpendicular to the rotatable driving shaftthat is polygonal, and formed by a plurality of planes.
 2. The processof claim 1, wherein a mixture of the materials to be separated isroughly shredded to a particle size of ≦50 mm.
 3. The process of claim1, wherein the fibrous material is defiberized in a casing, and thedefiberized material is discharged through borings or outlets in ajacket surface of said casing, while the viscoplastic materials remainin the casing, being withdrawn as a separate flow at an end thereof. 4.The process of claim 3, wherein the defiberizing effect is enhanced bysharp edges arranged at the borings or outlets at one interior surfaceof said casing.
 5. The process of claim 3, wherein materialflow/transport in said casing results from the direct influence ofblades producing radial, axial and tangential acceleration forces. 6.The process of claim 1, wherein said device includes a box having acharging inlet and an outlet in which said screen basket is arranged. 7.A device for the dry separation of viscoplastic materials from materialsdefiberizing under mechanical stress, consisting of a screen baskethaving borings or outlets in a jacket, allowing the defiberized materialto pass through, a rotatable driving shaft being arranged coaxially inan inner zone of the screen basket, with blades being attached in rigidconnection and orthogonal to said driving shaft, so that depending onthe number of blades, an inclination of the blades and a length of thescreen basket only the fibrous material will be defiberized andseparated from the viscoplastic material, the viscoplastic materialsbeing withdrawn in an essentially non-shredded state in a separate massflow, wherein the screen basket has a cross section in a planeperpendicular to the rotatable driving shaft that is polygonal, andformed by a plurality of planes.
 8. The device of claim 7, wherein saidblades are attached to said driving shaft at an inclination angle of 5-7degrees, wherein said inclination angle is an angle between a fixedreference line in said blade profile and a plane which is orthogonal tosaid driving shaft.
 9. The device of claim 7, wherein said blades near acharging side are smaller in diameter than said blades near adischarging side.
 10. The device of claim 7, wherein said blades arearranged on the driving shaft in such way as to leave a gap betweenblade ends and the screen basket.
 11. The device of claim 7, whereinsaid screen basket with interior rotatable driving shaft and blades isarranged in a box having a charging inlet at a charging side for themixture of materials to be separated, and an outlet at another end forthe plastics remaining in the drum and being conveyed by the rotatingblades.
 12. The process of claim 7, wherein said device includes a boxhaving a charging inlet and an outlet in which said screen basket isarranged.
 13. The device of claim 7, wherein said blades are attached tosaid driving shaft at such an inclination angle to ensure motion of saidmaterials to be separated in an axial direction.
 14. A process for thedry separation of viscoplastic materials from materials defiberizingunder mechanical stress, wherein the materials to be separated aresubjected to high acceleration and impact forces in radial, axial andtangential directions, and a mass flow of fibrous material and a massflow of viscoplastic materials are withdrawn separately, and whereinsaid viscoplastic materials and said materials defiberizing undermechanical stress are present essentially as composite materials, andonly the fibrous material will be defiberized under the action of saidforces and separated from the viscoplastic material, the viscoplasticmaterials being withdrawn in said mass flow in an essentiallynon-shredded state, wherein said high acceleration and impact forces areimparted with a device consisting of a screen basket having borings oroutlets in a jacket, allowing the defiberized material to pass through,the borings at one interior surface of the screen basket having sharpedges to enhance the defiberizing effect, a rotatable driving shaftbeing arranged coaxially in an inner zone of the screen basket, withblades being attached to said driving shaft, so that depending on thenumber of blades, an inclination of the blades and a length of thescreen basket only the fibrous material will be defiberized andseparated from the viscoplastic material, the viscoplastic materialsbeing withdrawn in an essentially non-shredded state in a separate massflow, wherein the screen basket has a cross section in a planeperpendicular to the rotatable driving shaft that is polygonal, andformed by a plurality of planes.
 15. The process of claim 14, wherein amixture of the materials to be separated is roughly shredded to aparticle size of ≦50 mm.
 16. The process of claim 14, wherein thefibrous material is defiberized in a casing, and the defiberizedmaterial is discharged through borings or outlets in a jacket surface ofsaid casing, while the viscoplastic materials remain in the casing,being withdrawn as a separate flow at an end thereof.
 17. The process ofclaim 16, wherein the defiberizing effect is enhanced by sharp edgesarranged at the borings or outlets at one interior surface of saidcasing.
 18. The process of claim 16, wherein material flow/transport insaid casing results from the direct influence of blades producingradial, axial and tangential acceleration forces.
 19. The process ofclaim 14, wherein said device includes a box having a charging inlet andan outlet in which said screen basket is arranged.
 20. A device for thedry separation of viscoplastic materials from materials defiberizingunder mechanical stress, consisting of a screen basket having borings oroutlets in a jacket, allowing the defiberized material to pass through,the borings at one interior surface of the screen basket having sharpedges to enhance the defiberizing effect, a rotatable driving shaftbeing arranged coaxially in an inner zone of the screen basket, withblades being attached in rigid connection and orthogonal to said drivingshaft, a rotational speed of said blades being adjustable within a rangeof from 1000 to 2000 rpm, so that depending on the number of blades, aninclination of the blades and a length of the screen basket only thefibrous material will be defiberized and separated from the viscoplasticmaterial, the viscoplastic materials being withdrawn in an essentiallynon-shredded state in a separate mass flow, wherein the screen baskethas a cross section in a plane perpendicular to the rotatable drivingshaft that is polygonal, and formed by a plurality of planes.
 21. Thedevice of claim 20, wherein said blades are attached to said drivingshaft at an inclination angle of 5-7 degrees, wherein said inclinationangle is an angle between a fixed reference line in said blade profileand a plane which is orthogonal to said driving shaft.
 22. The device ofclaim 20, wherein said blades near a charging side are smaller indiameter than said blades near a discharging side.
 23. The device ofclaim 20, wherein said blades are arranged on the driving shaft in suchway as to leave a gap between blade ends and the screen basket.
 24. Thedevice of claim 20, wherein said screen basket with interior rotatabledriving shaft and blades is arranged in a box having a charging inlet ata charging side for the mixture of materials to be separated, and anoutlet at another end for the viscoplastic materials remaining in thedrum and being conveyed by the rotating blades.
 25. The process of claim20, wherein said device includes a box having a charging inlet and anoutlet in which said screen basket is arranged.
 26. The device of claim20, wherein said blades are attached to said driving shaft at such aninclination angle to ensure motion of said materials to be separated inan axial direction.
 27. A process for the dry separation of viscoplasticmaterials from materials defiberizing under mechanical stress, whereinthe materials to be separated are subjected to high acceleration andimpact forces in radial, axial and tangential directions, and a massflow of fibrous material and a mass flow of viscoplastic materials arewithdrawn separately, and wherein said viscoplastic materials and saidmaterials defiberizing under mechanical stress are present essentiallyas composite materials, and only the fibrous material will bedefiberized under the action of said forces and separated from theviscoplastic material, the viscoplastic materials being withdrawn in aseparate mass flow in an essentially non-shredded state, wherein saidhigh acceleration and impact forces are imparted with a deviceconsisting of a screen basket having borings or outlets in a jacket,allowing the defiberized material to pass through, the borings at oneinterior surface of the screen basket having sharp edges to enhance thedefiberizing effect, a rotatable driving shaft being arranged coaxiallyin an inner zone of the screen basket, with blades being attached tosaid driving shaft, a rotational speed of said blades being within arange of from 1000 to 2000 rpm, so that depending on the number ofblades, an inclination of the blades and a length of the screen basketonly the fibrous material will be defiberized and separated from theviscoplastic material, wherein the screen basket has a cross section ina plane perpendicular to the rotatable driving shaft that is polygonal,and formed by a plurality of planes.
 28. The process of claim 27,wherein a mixture of the materials to be separated is roughly shreddedto a particle size of ≦50 mm.
 29. The process of claim 28, whereinmaterial flow/transport in said casing results from the direct influenceof devices producing aid radial, axial and tangential accelerationforces.
 30. The process of claim 27, wherein the fibrous material isdefiberized in a casing, and the defiberized material is dischargedthrough borings or outlets in a jacket surface of said casing, while theviscoplastic materials remain in the casing, being withdrawn as aseparate flow at an end thereof.
 31. The process of claim 27, whereinsaid device includes a box having a charging inlet and an outlet inwhich said screen basket is arranged.
 32. A device for the dryseparation of viscoplastic materials from materials defiberizing undermechanical stress, consisting of a screen basket having borings oroutlets in a jacket, allowing the defiberized material to pass through,the borings at one interior surface of the screen basket having sharpedges to enhance the defiberizing effect, a rotatable driving shaftbeing arranged coaxially in an inner zone of the screen basket, withblades being attached in rigid connection and orthogonal to said drivingshaft, a rotational speed of said blades being within a range of from1000 to 2000 rpm, so that depending on the number of blades, aninclination of the blades and a length of the screen basket only thefibrous material will be defiberized and separated from the viscoplasticmaterial, the viscoplastic materials being withdrawn in an essentiallynon-shredded state in a separate mass flow, wherein the screen baskethas a cross section in a plane perpendicular to the rotatable drivingshaft that is polygonal, and formed by a plurality of planes.
 33. Thedevice of claim 32, wherein said blades are attached to said drivingshaft at an inclination angle of 5-7 degrees, wherein said inclinationangle is an angle between a fixed reference line in said blade profileand a plane which is orthogonal to said driving shaft.
 34. The device ofclaim 32, wherein said blades near a charging side are smaller indiameter than said blades near a discharging side.
 35. The device ofclaim 32, wherein said blades are arranged on the driving shaft in suchway as to leave a gap between blade ends and the screen basket.
 36. Thedevice of claim 32, wherein said screen basket with interior rotatabledriving shaft and blades is arranged in a box having a charging inlet ata charging side for the mixture of materials to be separated, and anoutlet at another end for the plastics remaining in the drum and beingconveyed by the rotating blades.
 37. The device of claim 32, whereinsaid blades are attached to said driving shaft at such an inclinationangle to ensure motion of said materials to be separated in an axialdirection.
 38. The device of claim 32, wherein said device furthercomprises a box having a charging inlet and an outlet in which saidscreen basket is arranged.